The present invention relates to a composite pre-preg which exhibits desired electrical properties without loss of structural integrity or the addition of parasitic weight, and a method of preparing the composite prepreg ply.
Articles fabricated from fiber reinforced resin matrix composite materials are known, and have found increasing use in load bearing structural applications due to their high strength, light weight, and ability to be fashioned into complex shapes. Such composite structural materials are particularly suitable for aircraft structures.
In many aerospace and electronics applications, including EMI shielding/attenuation, antennas, aircraft structures components and anechoic chambers, it is desirable to impart certain electrical properties to the composite structure. It is further desirable to provide a composite structure with rather complex electrical properties where various dielectric constants are desired to be located in close proximity and in a particularly tailored pattern or design.
In conventional applications where dielectric tailoring is desired, a plurality of prepegs are formed such that each has a desired dielectric constant. Each prepreg is then cut to the final shape and assembled in a lay up such that the final composite component exhibits the desired dielectric constant in the desired area. Disadvantageously, each dielectric constant area is a separate prepreg which has been placed next to others during layup. This xe2x80x9ccut and pastexe2x80x9d arrangement, although exhibiting the desired dielectric constant pattern, cannot exhibit structural properties of a single substrate having a continues fiber orientation. Moreover, forming a single component from multiple pieces suffers from other disadvantages, including the addition of parasitic weight, secondary processing complications, increased layup costs due to the inclusion and assembly of many pieces, and limitation to discrete regions each of which define a single dielectric constant.
Accordingly, it is desirable to provide a method facilitating the manufacture of a composite structure providing multiple different dielectric constant regions without reducing structural integrity. It is further desirable to provide a composite structure which exhibits a graduated dielectric constant profile rather than discrete areas of a single dielectric constant.
A structurally dielectrically tailored prepreg panel or component according to the present invention provides a 2-dimensional dielectrically tailored (2DDT) structural material having desired electrical qualities in one or more desired areas of the prepreg without loss of structural integrity or the addition of parasitic weight.
In one method of manufacture a prepreg having predetermined dielectric properties is at least partially covered by a mask. An applicator such as a spray nozzle will then apply a first dielectric material to a first area not covered by the mask. In this method the dielectric material is substantially the same impregnating resin used in the original manufacture of the prepreg but having a different dielectric constant. The first area provides a dielectric constant different than the original prepreg. The process may then be repeated with any number of masks and dielectric materials until the final dielectric design of the prepreg is complete.
Another 2DDT manufacturing process again begins with a prepreg having a predetermined dielectric property. As the prepreg already includes a fiber reinforcement substrate with a formulated impregnating resin in a yet as uncured form, the impregnating resin provides a tacky or adherent surface. In this embodiment, the dielectric material includes a dry material which sticks to the impregnating resin such as a plurality of impurities that can change the dielectric properties of the resin.
The above embodiments alternatively or additionally provide for a continuously graded change of the dielectric content. Multiple dispensers and/or control of the dielectric material and applied volume percentage of each material will provide a dielectric gradient. The volume percentages of one or more dielectric materials having a single predetermined dielectric constant when applied at a certain volume percentage per unit area are applied in other volume percentages to achieve a much greater dielectric constant variation. A graduated dielectric constant rather than a discrete dielectric constant area is therefore provided.
In another embodiment an applicator arrangement 32 includes a plurality of applicators arranged to form a multiple of applicator sets. Each applicator set includes a multiple of applicators each of which dispense a particular dielectric resin. The applicator arrangement preferably communicates with a controller to selectively activate a particular applicator and dispense a desired dielectric resin in a desired location. Preferably, only a single pass of the applicator arrangement is required to manufacture the 2DDT material. The applicator arrangement dispenses the desired dielectric resins directly to a substrate or to a release film for later application to the substrate.
The present invention therefore provides a system and method providing multiple different dielectric constant regions without reducing structural integrity. Further the dielectric constant regions may be of a graduated dielectric constant profile rather than discrete areas of a single dielectric constant.